My point was that you can't use the same difference when comparing an SS to essentially a blown SS. Sure, the V package may add on 400 lbs to a base V6 CTS, but it won't add 400 lbs to a V8 SS that already has big heavy brakes and wheels. There's a much greater difference between the V package and a base CTS than there will be between an SS and a Z28, and some of it will be lighter (ie brakes).
I see what you're saying, but I'm comparing a base V6 Camaro to a base V6 CTS. I don't think the Z28 will weigh as much as a CTS-V, but IMO, it will be close to the 4100lb mark if not a bit more.
The V6 Camaro without big wheels and brakes, (what maybe 40lbs"?) is still just as heavy as the V6 CTS sedan.
Hell, if you look at the difference between a Z06 and ZR1 it's still 200lbs+ and they used more carbon fiber to keep it light. Despite the shipping weight of your aftermarket blower I don't think that indicative of what the new z28 will weigh.